Generally, in order to obtain resonance at different frequencies in an antenna device, it is only necessary to provide the antenna device with antenna elements as many as the number of the different frequencies and a transmitting/receiving circuit for causing the antenna elements to operate. However, it is necessary to secure a large space in an antenna device so as to provide an additional antenna element and a transmitting/receiving circuit. Namely, as the number of frequencies at which resonance occurs increases in an antenna device, the antenna device becomes larger.
In view of the circumstances, ways and means to miniaturize an antenna device while obtaining resonance at different frequencies have been suggested.
For example, Patent Literature 1 discloses an antenna device which causes a switch to connect/disconnect two antenna elements with/from each other.
According to the antenna device disclosed in Patent Literature 1, a change made by the switch causes the antenna device to resonate with signals of two kinds of frequencies by changing a substantial length (hereinafter referred to as an electrical length) of an antenna operating as an antenna, so as to miniaturize the antenna device by causing circuits required to be provided for respective antenna elements to be shared.